1
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1answer
68 views

Gravitational Force (conceptual) [duplicate]

Why is gravitational force always an attractive force? And is the Newtonian formula of gravitational force applicable for very small particles like electrons and protons etc.? From Formula of ...
3
votes
2answers
93 views

What does an applied force on an already accelerating object do?

I'm a big beginner having only taken Grade 11 high-school physics. Imagine this situation: an object is accelerating north, and while it's accelerating, it's 'hit' by a northward force. To me it ...
0
votes
3answers
49 views

Solving for Normal Force

I'm working through The Nature of Code, which is an awesome book, lots of fun. I've come across Exercise 3.13 and I'm not sure how to solve it. I'm assuming that the force of gravity and the force of ...
1
vote
3answers
37 views

In this particular problem: Is the mass of the system the mass of the person?

I am doing this problem: The upward normal force exerted by the floor is 620 N on an elevator passenger who weighs 650 N. What is the magnitude of the acceleration? This is how I solved ...
1
vote
1answer
49 views

Help for orbits of planets

Suppose that an asteroid) that moves at a velocity $v$ passes near to a planet: now I know that the gravity force of the planet will curve the trajectory of the asteroid so I tried to make a draw of ...
2
votes
4answers
215 views

Why Newton's law of universal gravitation is a valid law? What causes any two bodies in the universe attract each other with a force?

Why Newton's law of universal gravitation is a valid law? What causes any two bodies in the universe attract each other with a force? What causes a larger body in space to have a gravitational pull on ...
5
votes
2answers
294 views

Does the mass of a star change as it collapses into a black hole?

I know (I think!) that when a really big star collapses on itself it creates a black hole. My question: When a star collapses, is the mass equal to the mass of the star when it's not a black hole? Or ...
0
votes
3answers
174 views

Gravity force between two objects with different mass

We know thanks to Newton that: $$F=G\frac{m_1\cdot m_2}{r^2}$$ Where $G$ is the Gravitational Constant that is about $6.673\cdot10^{-11}$ $m_1$ and $m_2$ are the masses of two different objects ...
0
votes
6answers
195 views

Is gravitational force affected by intervening medium?

If we leave a iron ball and feather into the water, feather returns to the surface and floats or moves into the water slowly. On the other hand, iron ball (of certain mass greater than mass of ...
18
votes
3answers
2k views

How is gravity consistent when you split an object into multiple pieces?

Here's the picture: In picture 1: Assume that we have 2 objects, namely A, and B. Object A with mass $2M$, and object B with mass $m$; and their distance is $r$. Then the gravitational force of A ...
1
vote
4answers
131 views

Can you lift yourself standing on a wooden block using pulley mounted on block? [duplicate]

I am new to this site. Please help me figure out this problem. Is it possible to lift oneself like shown in schematic? Waiting for good suggestions. Chirag
38
votes
6answers
5k views

Pouring water in an aircraft while upside down?

What is the physics behind the following photo? Someone had told me that this is because the aircraft might be moving towards a lower altitude, but I am still not sure.
3
votes
1answer
84 views

Pendulum in a Turning Airplane

My friend and I are having an argument over what happens with a pendulum hanging inside an airplane during a turn. Assuming that the airplane is making a standard 1 G coordinated turn, how does the ...
0
votes
1answer
221 views

Does the tension of a rope/cable change if acceleration/velocity changes?

For example, imagine an object of a certain mass which is attached to a rope and is dangling in the air. The rope needs to have a certain tension to be able to hold the object up, that is, negate the ...
0
votes
2answers
63 views

Can we feel our own weight (can we feel normal reaction)?

If we place something on our head, we can feel it's weight pushing us down. But we ourselves apply normal reaction which balances the weight of the object and stops it from actually pushing us down. ...
-3
votes
1answer
65 views

Forces: why are the theta's equal?

I found this figure in my physics book, the task says that the incline got a angle of theta. How do figure out that the gravity and the y-axis got the same angle as the incline? There is no ...
1
vote
3answers
128 views

How much up will an object of mass $m$ will be vertically lifted if a constant acceleration $a$ is given so that resulting force is more than weight?

Yesterday My friend asked me a question which put me into a confused state. If a body of mass m is given a vertical thrust of $F$ such that $F > mg$, and the $F$ is allowed to remain applied on ...
1
vote
0answers
149 views

Force from a HEMIspherical shell [closed]

I am working on this problem and just trying to figure out what my prof/ TA did in the solution sheet -- but also to make sure I understand what I am doing and some of the mathematics involved. A ...
0
votes
2answers
157 views

Equilibrium - uniform circular motion

Maybe this is a bit of a silly question, but let us pretend we have a pendulum in a ideal universe with no friction, drag, or anomalous forces there to affect it. Additionally, our pendulum is ...
1
vote
1answer
378 views

Newton's second law, gravity and buoyancy [closed]

A body of mass $m$ and volume $V$ is immersed into the sea. The body moves under the action of two forces: gravity and buoyancy (Archimedes). Gravity force has a magnitude $mg$, where $g$ is a ...
-2
votes
2answers
323 views

Explain what happens to object in lift [closed]

In the following image,three cases have been mentioned. $N$ is the normal force acting on the object inside the lift and $mg$ is the force of attraction due to gravity. In case 1, $N = mg$. In case ...
-2
votes
3answers
329 views

Why does a bicycle come to rest after travelling a distance?

According to Newton's law of motion, an object that is in motion will not change its velocity unless an external force acts upon it. In the case of a bicycle, if it is in motion with a certain ...
0
votes
2answers
647 views

What is going on in the system? How are the formulas `mg sin(x)` and `mg cos(x)` derived?

When a load is resting on an inclined plane, there is force $mg \sin(x)$ that's vertical to the inclined plane and force $mg \cos(x)$ horizontal to the plane acting on it like this: My textbook ...
0
votes
1answer
67 views

Combine forces (gravity)

I have a point at which there are (at least) two different forces (gravity to be precise) working. How do I combine those so that the force acting on the point are as realistic as possible? To put ...
1
vote
1answer
172 views

Thought experiment-shell theorem

Consider a uniformly dense perfectly spherical planet. At any point inside the planet, the gravitational attraction is only due to the mass below the point. (red circle) according to shell theorem. ...
0
votes
3answers
86 views

Is it possible to reach the edge of a room if there isn't any gravitational acceleration?

Consider that a large room(an indoor badminton court) is orbiting the earth with a person floating exactly at its center without any relative initial velocity. Consider that the person has no ...
2
votes
1answer
321 views

What if exactly half the Earth's population jumped at one instant? + Secondary Question

I read somewhere that when you jump, the sole effect caused by your jump on the earth moves it about $10^{-18}m$ (I don't remember the figure exactly, but I think it was that). However - obviously ...
-1
votes
1answer
89 views

Force-Weight Pinewood Derby Car [closed]

Force-Weight Pinewood Derby Car. I'm trying to make a fast derby car. I was wondering if I could make a car that can drop/eject weight once it comes off of the incline. Would that increase speed or ...
0
votes
0answers
130 views

Does the earth really move round the sun? [duplicate]

Is there really any empirical proof that the earth moves round the sun? I've read simple explanations using mass-gravity relation. But then some questions remain, is gravity a function of mass alone? ...
0
votes
1answer
219 views

Calculate magnitude of force acting on some area by falling object

I have simple question: is it possible to calculate magnitude of force acting on some area by falling object? Let's say I have an object with mass $5\text{ kg}$. I drop that object in height 1 ...
2
votes
1answer
154 views

Understanding Kepler's problem

I wanted to know a few things about elliptical motion, that I do not understand so far. Let's imagine that we have an attractive gravitational two body problem where both bodies carry out elliptical ...
2
votes
1answer
71 views

Falling through the ground [duplicate]

I do not know much about physics but I know that according to Newtons third law of motion when we walk we are pushing the ground down but the ground is pushing us up. What force is making the ground ...
0
votes
3answers
3k views

Force inversely proportional to the squared distance

Newton's law of universal gravitation: "Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to ...
6
votes
1answer
720 views

Slinky base does not immediately fall due to gravity

Why does the base of this slinky not fall immediately to gravity. My guess is tension in the springs is a force > mass*gravity but even then it is dumbfounding.
0
votes
1answer
707 views

If 2 charges have the same sign, the coulomb force is positive but repulsive, while with 2 masses the gravitational force is positive but attractive

If you have two point objects both the same positive charge and both of the same mass at a distance $r$ from each other. The force between them due to gravity is $F_g=\frac{Gmm}{r^2}$ and $F_g$ is ...
2
votes
1answer
97 views

Forces: Worth worrying anything?

I am a general physics student, I had a question in my text-book and according to it two students having gravitational attraction between them = ($6.67\cdot10^-8\ \mathrm{Nm}^2/\mathrm{kg}^2$) is not ...
1
vote
1answer
475 views

Gravity force strength in 1D, 2D, 3D and higher spatial dimensions

Let's say that we want to measure the gravity force in 1D, 2D, 3D and higher spatial dimensions. Will we get the same force strength in the first 3 dimensions and then it will go up? How about if ...
6
votes
2answers
227 views

Is it possible to use a balloon to float so high in the atmosphere that you can be gravitationally pulled towards a satellite?

A recent joke on the comedy panel show 8 out of 10 cats prompted this question. I'm pretty sure the answer's no, but hopefully someone can surprise me. If you put a person in a balloon, such that ...
2
votes
3answers
295 views

Weightlessness by a parabolic flight

Do you actually achieve weightlessness during a parabolic flight? Because I believe I heard somewhere did you achieve 'near-weightlessness' and not 'weightlessness' (if this is true, why is this?) ...
6
votes
3answers
841 views

Differences between the gravitational constants $G$ and $g$?

There's a formula (described by Sir Isaac Newton) that gives the force acting between two objects: $$F = \frac{Gm_1m_2}{r^2}$$ And then there's a formula for weight of an object $$w = mg$$ My ...
0
votes
0answers
21 views

Helpful tutorials on force [duplicate]

Possible Duplicate: List of good classical physics books I'm having a hard time understanding force in my highschool AP physics class, i looked through youtube but without luck. Could ...
57
votes
7answers
4k views

Does juggling balls reduce the total weight of the juggler and balls?

A friend offered me a brain teaser to which the solution involves a $195$ pound man juggling two $3$-pound balls to traverse a bridge having a maximum capacity of only $200$ pounds. He explained that ...
3
votes
1answer
296 views

Would the Moon drift away from the Earth due to extraction of tidal energy? [duplicate]

Possible Duplicate: Why does the moon drift away from earth? It seems to me that, due to conservation of energy, the moon would drift away from the Earth if humans began extracting large ...
0
votes
2answers
376 views

Hanging a Hammock

I have a hammock that I want to hang using a tree on one end and a wooden post set in a bucket of cement on the other end. How would I determine how heavy the cement needs to be so that it would ...
0
votes
4answers
1k views

Questions from elevator ride

I like to play inside the lift (elevator). For instance, there are bars attached at the side of the lift, and I like to hold my body up using my two hands on the bar. I realised that I actually feel ...
4
votes
1answer
697 views

Combining Proportions to get Newton's Law of Universal Gravitation

I've read a little on the history of Newton's Law of Gravitation and noticed that the formula can be separated into 3 distinct parts that lead to the end result of $F_g = G \frac{m_1 m_2}{r^2}$; the ...
1
vote
1answer
207 views

How do I factor in multiple forces into these Newtonian mechanics equations?

Say a person is walking along. He then jumps. The person weighs $25$kg (irrelevant?). Just after jumping, his velocity is 5m/s (positive is taken as up). Gravity is taken as ...
1
vote
2answers
342 views

The two-body problem: What is force between them?

Two bodies with similar/different mass orbiting around a common barycenter. What is force between them, where $F_{12}$ is the force on mass 1 due to its interactions with mass 2 and $F_{21}$ is the ...
5
votes
4answers
939 views

what is the 2D gravity potential?

In 3D, I can calculate the total force due to gravity acting on a point on the surface of the unit sphere of constant density, where I choose units so that all physical constants (as well as the ...
2
votes
1answer
192 views

Does a slinky hanging downward double in length if gravity doubles?

Also would a spring under tension greater than the force of gravity pulling the spring downward shrink in both directions until it has depleted it's stored energy while in free fall?